#include <stdio.h>
#include <math.h>

int main(int argc, char *argv[]) {

    int x1, y1, x2, y2;
    while (scanf("%d %d %d %d",&x1,&y1,&x2,&y2)!=EOF)
    {
        int h = abs(y2 - y1);
        int l = abs(x2 - x1);

        double x = sqrt(pow(h, 2) + pow(l, 2));
        printf("%.2lf\n", x);
    }
    

    return 0;
}